Conventionally, vehicles are equipped with seat belt apparatuses for restraining occupants each of which prevents the occupant from being thrown forward due to an inertial force when an impact is generated, for example, at the time of a rapid deceleration or a collision of the vehicle. Such a seat belt apparatus is generally provided with an Emergency Locking Retractor (hereinafter, referred to as an ELR) which does not restrain motion of the occupant in normal driving but locks a winding shaft for the seat belt to prevent the seat belt from being further withdrawn only when an impact is generated to the vehicle. The ELR locks the winding shaft within a very short time after detecting a deceleration equal to or higher than a predetermined value, thereby preventing the seat belt from being further withdrawn.
However, according to the aforementioned ELR which merely locks the winding shaft, in case where the seat belt is loosely wound onto the winding shaft when worn by the occupant, a certain amount of the seat belt may be withdrawn even when the winding shaft is locked. Even when the seat belt is not loosely wound, the seat belt may still be withdrawn between the time of detection of a deceleration equal to or higher than the predetermined value and the time of locking of the winding shaft.
As a device for canceling the looseness of the seat belt and the withdrawal of the seat belt caused by the time lag until the winding shaft is locked to some extent, there is known a pretensioner which retracts the seat belt buckle when a predetermined deceleration is detected (see Patent document 1, for example).
The pretensioner as disclosed in Patent document 1 comprises a wire of which one end is connected to a seat belt buckle and the other end is fixed to a piston in a cylinder and a housing through which the wire is passed and which supports the cylinder. According to this pretensioner, when a deceleration of the vehicle is detected, high-pressure gas is spouted into a gas chamber formed in the housing so as to move the piston, thereby retracting the wire. In the gas chamber of the housing, a guide pipe is disposed to protect the wire from the high-pressure gas. In the housing, a packing for sealing a clearance between the wire and the housing is disposed adjacent to the guide pipe.
Patent document 1: JP-A-2003-146184 (FIG. 2 and FIG. 4).